Date of Completion

5-9-2015

Embargo Period

5-4-2015

Advisors

Xinyu Zhao, Michael W. Renfro

Field of Study

Mechanical Engineering

Degree

Master of Science

Open Access

Open Access

Abstract

Extinction of 1-D laminar non-premixed counterflow flames and a 3-D turbulent non-premixed ethylene jet flame into air coflow is studied with chemical explosive mode analysis (CEMA), which is an eigen-analysis shown to be effective in systematic detection of critical flame features in a variety of combustion systems, e.g. auto-ignition, ignition and extinction in perfectly stirred reactors, and location of premixed reaction fronts. In the present study, CEMA-based criteria are proposed to systematically detect local extinction and re-ignition in non-premixed flames. The method is first demonstrated with 1-D laminar counterflow flames showing that mixtures in the reaction zone start to show explosive behavior, characterized by a positive eigenvalue of the chemical Jacobian, when the flame approaches extinction as strain rate increases, while only nonexplosive mixtures are present in strongly burning flames at low strain rates. Thus the existence of explosive mixtures provides a necessary condition to detect flame extinction. This criterion is further employed to study the direct numerical simulation (DNS) data from a 3-D non-premixed temporal turbulent ethylene-air jet flame. Local subdomains with strongly burning non-premixed flamelet, and near-extinction and post-extinction features are identified and investigated using CEMA-based diagnostics. Propagating premixed flame fronts are also identified in the re-ignition process of the globally non-premixed flame.

Major Advisor

Tianfeng Lu

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